It is well known in the art to provide a door with a deadbolt lock. Such locks are generally provided where security is a concern, such as the door of a home, business, or hotel room. The lock is operable by key on the outside. It may be operable without a key on the inside by a simple knob. This enables escape in an emergency without a key. The knob is elliptical in shape so that a user can visually determine whether the deadbolt is locked or unlocked. The long axis of the ellipse is generally vertical when the bolt is in the locked position. When a person is secure behind a deadbolt locked door, that security may be breached by someone with a key, or someone with means to retract the bolt. It would be useful to provide means to further ensure that someone with a key or such means could not unlock the door.